The private investigator who testified last week before special prosecutor Kenneth Starr's grand jury and has been likened to President Clinton's private CIA, is a man of enormous extremes and contradictions, according to friend and foe alike.

He's an Exeter-and-Harvard-trained lawyer who tossed over corporate law for corporate and political gumshoeing; a devoted and protective father who's left a trail of enemies in his professional life; a cardiac bypass veteran who pops nitroglycerine pills before marathon tennis games that he treats like holy wars.

He has fought organized crime as a U.S. attorney in New York and defended antiwar activist Philip Berrigan on charges of plotting to kidnap Henry Kissinger. He's been a zoning attorney for Conrad Cafritz and documented rumors of a sexual assault on a teenage babysitter that then loomed large in a U.S. Senate campaign in Maine.

"Terry is a very, very complex man," says a Cleveland Park neighbor who claims long friendship. "He's a perfect Type A personality: smart, aggressive, obsessive and more than a little paranoid. He's got a sense of humor and unlike so many people in Washington he's not consumed by self-importance. But God help you -- and I really mean that -- if you're on the other side. He's got a dark side that's pretty scary."

Lenzner himself declined to be interviewed for this story. But Monroe Price, a professor at Cardozo Law School in New York who has known Lenzner since the 1960s, says, "My image of Terry is the boyish charm of the guy who was captain of the Harvard football team and always saw that in a larger context . . . sort of the last real citizen-athlete. Maybe he just always needs to be captain."

In a Washington legal community that often appears overfed and stultifying, Terry Falk Lenzner, 58, moves with the black-hat swagger of the maverick hired gun. His friends say it's an overdrawn image, sharply at odds with his past as a Justice Department civil rights attorney in the 1960s, a onetime member of Harvard's board of overseers, and the president of a modest family foundation that last year scattered $42,500 among 36 schools and charities ranging from Bennington College to the House of Ruth.

Yet Investigative Group Inc. (IGI), the firm he founded 14 years ago after a fractious decade in corporate law, ranks as a major strike force among the nation's swelling legions of button-down dirt diggers. Claiming cyber-savvy expertise and access to 140,000 databases as well as near global reach on behalf of its clients, IGI has been retained for everything from checking out potential business partners in the former Soviet Union (he's hired former KGB agents to help with that) to helping would-be professors unlock the tightly held secrets of earning academic tenure at Harvard. According to the Wall Street Journal, he was even hired by Ivana Trump to investigate her rival, Marla Maples.

Though his investigations regularly turn up material not available in the public record -- such as phone records and credit card receipts -- Lenzner contends he never does anything illegal or unethical on behalf of his clients.

And though corporate clients pay most of the IGI bills, former employees say, Lenzner's repeated and covert sleuthing on behalf of Clinton and other Democratic figures may loom largest in Lenzner's life.

Having headed the U.S. Office of Economic Opportunity's legal services program at age 29, and been a high-profile deputy counsel for the Senate Watergate Committee a few years later, Lenzner still looks wistfully toward some high-visibility government post, his friends say, particularly the directorship of the FBI.

"But he's never been able to nourish and maintain the necessary network of personal and political alliances long enough to make that happen," says one longtime colleague, who like almost everyone interviewed about Lenzner declined to speak on the record. "He's a natural leader and he's smart as hell and he knows a lot of people. But his confrontational nature and scorched-earth tactics eventually turn people against him."

Ordinarily it might be difficult to evaluate such statements from people who refuse to speak for the record. But what may be unique about Lenzner is that his fans and detractors say almost exactly the same things.

Even his professional rivals and former employees embittered by his management style concede that Lenzner is never less than a brilliant investigator who invariably gives clients exactly what they want. Even his best friends contend that his volcanic intensity and deep-rooted insecurity repeatedly cause him problems.

The question that troubles both groups is whether, where and when those lifelines intersect. In the age of computer snooping and instant access, private investigators -- like the journalists who often join their staffs -- can focus their skills either to enlighten or to bully. Which mission these days, those who know him wonder, claims more of the considerable passions of Terry Lenzner?

Exhibit A in the minds of Lenzner critics is the case of Jeffrey Wigand, the former Brown & Williamson tobacco executive who turned against his former employers five years ago with explosive allegations of corporate wrongdoing. With the help of IGI, B&W attorneys compiled a massive 500-page file titled "The Misconduct of Jeffrey S. Wigand Available in the Public Record" that amounted to the gleanings of phone records, medical records, typographical errors and police blotter effluvia purporting to portray Wigand as a liar, shoplifter, plagiarist, wife-beater and expense-account cheater, among other categories of malfeasance.

The compilation, which Wigand's lawyer labled "a smear campaign," was remarkable enough that, when B&W representatives leaked it to the Wall Street Journal two years ago, the Journal made the investigation itself the story, noting that many of the serious allegations "are backed by scant or contradictory evidence" and some "are demonstrably untrue."

Lenzner told Fortune magazine last April that he was proud of IGI's contribution to the Wigand case but conceded that facts in the report "were not completely developed."

"Any investigator I respect would have walked out rather than take that kind of case," said one of Lenzner's ex-employees, who says he left in part because of incidents like the Wigand case. Increasingly, he contends, Lenzner has appeared willing to indulge a "viciousness" that has left onetime admirers "horrified by the transformation."

Equally troubling to some has been the cloudy identity of some of IGI's employers. When IGI investigators were discovered researching Sen. Edward Kennedy's opponent in 1994, the Kennedy campaign first denied employing Lenzner, then admitted it when confronted by the Boston Globe. When no record of payments to or donations by IGI turned up on Kennedy's campaign finance reports, it was finally discovered that Washington lawyer James Flug had hired IGI and been reimbursed by the campaign. Likewise, IGI investigators materialized in the 1994 gubernatorial race in Tennessee asking questions about Nashville Mayor Philip Bredesen, but refused to say whom they were working for.

The exact relationship between Lenzner and the Clinton White House has been similarly unclear, although Lenzner has been working at least since 1994 for Clinton lawyers in the Whitewater and Paula Jones cases, did work for the Democratic Party in 1997, and received a no-bid grant worth hundreds of thousands of dollars from the State Department in 1994 and 1995 to train police officers in Haiti, according to the Associated Press.

Among former IGI investigators is Brooke Shearer, a longtime Clinton friend and wife of Deputy Secretary of State (and Clinton's former Oxford University housemate) Strobe Talbott. Shearer traveled with Hillary Rodham Clinton in the 1992 campaign as a press aide and later worked in the Clinton White House.

The Associated Press reported last week that Secret Service entry logs show Lenzner himself visiting the White House a half-dozen times in recent years, including a 1996 meeting with ex-deputy chief of staff Harold Ickes to discuss potential investigative work.

For some of those who remember Lenzner as the aggressive deputy counsel of the Watergate Committee a generation ago -- the scourge of Richard Nixon's dirty tricksters -- what Lenzner appears to be doing now, in and out of politics, has begun to smell suspiciously like what he was once fighting against.

On one hand, the "opposition research" performed by private detectives like Lenzner, despite the tut-tutting with which it's recently been greeted in some corners of the press, is at least as old as Machiavelli and as American as apple pie. The great political novel of American literature, Robert Penn Warren's "All the King's Men," details the gradual inch-by-inch corruption of a failed idealist whose talent for "opposition research" eventually results in the loathsome political blackmail of a much-loved family friend.

But today's political snoops aren't the same, says one Lenzner admirer. Hill & Knowlton's Frank Mankiewicz, who served as Robert F. Kennedy's press secretary, hired Lenzner six years ago after H&K was retained by the United Way to handle inquiries into the lavish lifestyle of United Way President William Aramony.

Lenzner was told by the United Way to beat reporters to any problem areas so the charity could deal with them internally. But what he found was so damaging that Aramony eventually had to resign.

"I thought he did a great job and I'd recommend him to anybody," Mankiewicz said recently. But he says professional sleuths like Lenzner are a whole different animal than the "opposition researchers" of politics past.

"In the old days a congressman would have some old pol back in the home district with his ear to the ground for gossip about any potential candidates," Mankiewicz said. But however effective -- and brutal -- those investigators may have been, "they didn't have the background and the training, much less the technology, to go after things like phone records and the like."

The emergence of firms like IGI in politics "puts things on a whole new level," he says.

What concerns other friends of Lenzner, and former associates who describe themselves as disillusioned, is what they see as the dangers inherent in wedding the abusive potentialities of modern high-tech investigation methods with Lenzner's take-no-prisoners attitude.

"He's certainly not characterized by restraint," says one longtime acquaintance. Says another: "He's like a guy walking around with gasoline poured over him, just looking for a match."

Some see Lenzner's extraordinary drive, obsession with details and explosive temperament as defenses born of an excessively demanding father -- a wealthy Manhattan dentist and onetime college football star who bullied his sons into toughness.

Noting with genuine admiration Lenzner's 30-year marriage to his wife, Margaret, their million-dollar home in Cleveland Park and much-loved summer house in Nantucket, and Lenzner's devotion to his daughter and two sons, one friend says: "I've always believed he struggled to build for his own kids the kind of family life he wishes he'd had."

But equally important to his formative years, others say, was a childhood bout of rheumatic fever that immobilized the athletic youngster for nine months and left him nagged by fears of a permanently weakened heart. "Something happened to me lying there," Lenzner told an interviewer six years ago. "I guess it made me realize that I had to get things done quickly, that I needed to move."

He played football at Exeter, as at Harvard, and is famous in Washington for his morning workouts and relentless tennis matches. "I don't want to overdraw this, but he seems to brood on his own mortality," says one of his regular partners. "He takes these nitroglycerine pills before every tennis match. He's fanatical about what he eats. . . . It's like something's chasing him."

Lenzner was hired out of Harvard Law School by the Justice Department's civil rights chief John Doar, who was impressed by his drive and dedication. But his confrontational style produced frequent blow-ups with his immediate supervisor, Bob Owen. When Lenzner moved on to head the legal services office at OEO, he was fired after 18 months by Director Donald Rumsfeld, in part for such high-profile irritants as having OEO lawyers defend the Black Panthers in their armed confrontations with the New Orleans police.

When he was deputy counsel of the Senate Watergate Committee his aggressive tactics produced stormy scenes with another deputy counsel, James Hamilton, who believed civility in the course of investigation need not be a sign of weakness.

When Lenzner moved into private practice after Watergate, he stumbled onto a case tailor-made for his passions. An inquiry into disputed native Alaskan land claims snowballed into 10 years of litigation over corruption in the building of the Alaskan pipeline.

According to Legal Times, Lenzner, whose painstaking investigation documented evidence of contractors bilking the state of Alaska, earned some $12 million with the case. But it also propelled him into merging his small firm with Wald, Harkrader & Ross, then abruptly quitting that firm in 1981 to become a name partner at Rogovin, Huge & Lenzner, taking his hugely profitable litigation with him. Wald and Harkrader folded three years later.

In 1984 Lenzner branched off from his law partners to form IGI as a separate investigative unit. "Lawyers," he would later tell an interviewer, "are not well trained in obtaining facts." But his habit of spending time on IGI matters, but not sharing the profits with his law partners, led to an eventual departure from Rogovin, Huge in 1987, according to a 1992 profile in Washingtonian magazine.

In the years since then, IGI's triumphs have been accompanied by employee turnover, including the exit of two investigators, Jim Mintz and John Hanrahan, with whom Lenzner founded the firm. Former law partners and associates who have witnessed the various departures over the years blame the infamous Lenzner style.

Last week as Lenzner was in the news, New York Times columnist (and former Nixon staffer) William Safire took to his keyboard to remember Lenzner as a "bully" who pursued his work on the Watergate Committee with a "gleeful savagery" reminiscent of the McCarthy era. Two days later fellow columnist Frank Rich chastised him as a "creep" and "one of the most ruthless mercenaries of the tobacco industry" for his investigation of Wigand.

Monroe Price, while saying he can't speak to Lenzner's activities at IGI, protests that such portraits mischaracterize a complex man who "has never done things as an ideologue but because he genuinely believes they're good for the country."

Another Lenzner friend yesterday agreed: "None of that [in the Times columns] is really fair. Terry's so much more than that -- -so smart, so charismatic, so genuinely able, so tenacious in pursuit of what he thinks is right. It's just that . . . in the process he's often his own worst enemy."